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LIBRARY OF CONGRESS 



S nun ii ii i I'll in ii 

019 409 691 4 



Tfl 616 
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Copy 



1 



MMMM, Mi»TCT!©NS 

In regard to representing the ground to the Topographical Parties of the Coast Sur- 
vey, accompanied by scales of Shade and Specimens of Topographical details. 

The following rules, and the principles laid down in paragraphs 8 and 9 of the 
accompanying report, will be followed by the Topographical Parties of the Coast 

Survey : 

1. For a scale of T7 jjoc>> m e vertical distance between the horizontal'curves will be 6 metres. 

2. For a scale of zvhvis ■> me vertical distance between the horizontal curves will be 9 metres. 

3. For a scale of 4^5^, the vertical distance between the horizontal curves will be 12 metres. 

4. For a scale of goiyoo 1 tne vertical distance between the horizontal curves will be 18 metres. 

5. At a slope of T 7 ff , the vertical distance between the horizontal curves will be doubled. At a slope 
of f §, quadrupled. At a slope of \%, octupled. 

6. When the hachures are added the horizontal curves will be preserved by leaving a narrow white 
-space in their places between each set of hachures. . 



7. River or other banks varying in height from 2 to 10 metres, if steeper than a slope of jg, may, 
for all practical purposes, be supposed to have a slope of {§, and the hachures may be made one-half the 
thickness of the hachures of the printed scale of shades, or even less; but the proportion of black and 
white spaces must be the same as that on the printed scale. 

8. Besides the horizontal curves, all accidents should be drawn in in the field; the peaks above the 
highest horizontal curves should be represented by hachures, as well as hills of less height than the vertical 
distance between the horizontal curves. 

9. The heights of hills should be set down. 

10. The accompanying scales of shade and models for topographical details will be followed closely, 
as well in regard to thickness of stroke, size, &c, as to form. 

A. D. BACHE, 
Superintendent U. S. Coast Survey. 



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1^> 




Report to the Superintendent of the Coast Survey by A. A. Humphreys , Lieut. Topi. Engrs., Assist- 

Coast Survey. 

1. The method of shading hills, adopted by the French Commission in/ K ^^ besides being compli- 
cated from changing its principle beyond certain slopes, which vary with the scale of the map, makes the 
lower slopes ((he most important) so light that it is difficult to distinguish 5°, 10°, or 15° from each other. 

2. Col. Bonne's scale of shades, in which the intensities of shade increase in proportion to the sine of 
the angle of slope, has the same defect. The specimens of hills shaded by these methods, accompanying 
the report of the proceedings of the commission, it will be observed, have shades very much darker than 
the scales would give. All the French methods or scales have the same defect. 

3. Lehman's scale of shades, besides not representing slopes beyond 45°, and therefore depriving 
maps of the graphic effect desired, makes the slopes near 45° too dark, and does not well represent slopes 
lower than 5°, which it is necessary for us to represent distinctly. His scale is arbitrary; so indeed are, 
in a measure, all those adopted by various nations and individuals. 

4. We may then use a completely arbitrary scale, combining the good qualities of Lehman's and the 
French, by which the lower slopes may be readily distinguished from one another, and the graphic effect 
of the high slopes retained. The slopes 2 V , tV> \> are tne most frequently met with in those parts of our 
country not mountainous; ^, 2 Vj tV ? are a ^ so s l°P es m use f° r roads; the slopes t6~> to > to" > (6°> 11°> 16°, 
about,) it is important to distinguish between, for military purposes. 

5. At a slope of 6° about, or y'^ , the fire of artillery downwards is more effective than on a plain; 
the infantry fire down is powerful, but upwards it begins to lose effect; the charge of cavalry down begins 

to lose effect; indeed, it may be questioned if the upward charge also has not lost some of its effect. This- 

slope may be considered the limit of the legitimate use of the cavalry charge. 

10°, or 11° ( T V) As cavalry can only move in a gallop over ground of this slope, its charge is not 
effective. Upwards, infantry is not effective; downwards, it is; artillery fire is not to be depended on. 

15° or 16°, (fVO Limit of heavy infantry movements; fire down has some effect; limit of cav- 
alry movements; limit of artillery movements and fire. Light infantry effective. 

■ 25° or 26° , (j^ .) Light cavalry in single file can ascend and descend slowly, but not beyond this 
slope; it is the limit, therefore, of light cavalry movement; it is also the limit of light carriage movement; 
light infantry is still effective. 

35°, ( T V) Light infantry move over this ground with difficulty; limit, therefore, of effective use of 
light infantry. 

45°, ( T §*) Light infantry can climb this slope. 

60°, (y 5 .) According to the Aide Memoire, the 1st slope actually inaccessible to infantry. 

75° or 76°, (^|.) The shade for this slope is intended merely to represent slopes greater than 60°. 

G. The preceding slopes are those which it is of most importance to distinguish. From zero to 15^ 
or 25°, it is necessary to represent more slopes, and to represent them more distinctly than between 25° 
and 45°; between 25° and 45°, it is not of importance to distinguish nicely between every few degrees of 
slope; between 45° and 90°, we should also represent some slopes for graphic effect, such as for clay 
banks, river banks, rocks, precipices, &c, &c; but it is not necessary to distinguish readily between the 
different slopes; the shade may vary for graphic effect only. 



A 



7. Lehman's scale of shade is — 
Blk. space. White space. B. W. B. W. B. W. B. W. B. W. B. W. B. W. 

1 8 2 — 7 3—6 4 — 5 5 — 4 6 — 3 7 — 2 8 — 1 Black. 

5° 10° 15° 20° 25° 30° 35° 40° 45° 

Some of these slopes (20°, 30°, 40°) it is not important to distinguish from those 5° greater or 5° 
less, as there is no civil purpose for which they are particularly useful, nor do they form the limits of 
any military movements, which those 5° greater or less do. 

8. The scale then proposed, adapted to any part of our country, both for civil and military purposes, 
and affording the means of graphic representations of the relief of ground, is the following modification of 
Lehman: 



51k. White. 


B. W. 


B. W. 


B. W. 


B. W. 


B. W. 


B. W. 


B. W. 


B. W. 


1 — 10 


2—9 


3 — 8 


4—7 


5—6 


6 — 5 


7—4 


8 — 3 


9—2 


2\ or 2|° 


5° or 6° 


10° or 11° 


15° or 16° 


25° or 26J° 


35° 


45° 


60° 


75° 


or 


or 


or 


or 


or 


or 


or 


or 


or 


i 

50~ 


i 

T0~ 


2 

1 


3 

TO 


5 


7 
TO" 


1 
TO" 


1 
5 


1 
2-5 



9. A slope of j'q- is represented by the same thickness of stroke as that for £ v , but the distance be 
tween the strokes should be double that of ^, and so proportionably for any slopes less than ^\. 

10. By this scale the lighter slopes are represented well, and will be readily distinguished from each 
other; the difference in shade between any two noted above, being nearly the same as between the lower 
slopes of Lehman. According to Mr. Siborn, (an English translator of Lehman's treatise,) slopes between 
10° and 30°, represented according to Major Lehman's style, may be read by inspection to within 1°. 

11. The shades for the slopes below f^axe, by-this-scale, darker—than those of Lehman, (about a_ 
mean between the shade for the corresponding degree and the next shade above on the scale,) it being in- 
tended to represent more lower slopes than he does. These slopes are those we shall more frequently find 
among the hills of the coast; they are, besides, those of most importance in a military point of view. 
From 25° up, the shades are lighter than the corresponding shades of Lehman; the distinction between 
slopes is here of less importance. In this scale of shade the white space for slope of 75° does not become 
too small for practical use. 

A. A. HUMPHREYS, 
Lieut. Topi. Engrs., Assist. C. S. 



LIBRARY OF CONGRESS 



019 409 691 4 £> 



